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and look at anything JustinV said to me about trouble shooting a stubborn LH system.
Here are a few things to get you going.
The LH unit works like this:
1. When the key is put into "run" or "crank" you get +12v to pin 18 on the LH control unit. You need damn close to +12v (I think between 10v and 14v) for the unit to think the ignition is on.
2. When the ignition is switched to on (as above) pin 21 on the ECU goes to ground, which closes the "system" relay and provides +12v to the ECU, the fuel pump relay, and the air mass meter.
3. At this point, the fuel injection computer is "on." When there is a tach signal at pin 1, pin 17 goes to ground which powers the fuel injectors and the fuel pump.
4. With the tach signal, the injectors are pulsed via the ground output on pin 13. That is, the injectors always have +12v and are fired by grounding them.
There are two things you need to check. You must check the tach signal to the LH box - dunno what pin it is off the top of my head, but you need to verify you're getting 2-3VAC (NOT VDC) there. If you're not, the problem is either your tach, the ignition module, or the Hall-Effect sensor. Given you've got spark, it probably isn't the Hall Sensor. You need to check to be sure that the switched power pin keeps its +12v during cranking - it should, but check it anyway.
After that, verify that both 87a and 87b on the fuel pump relay are working. You can make a little jumper wire with 3 ends to it, and connect one to pin 30, one to pin 87a and one to 87b on the pump relay. Need to have all three connected together. Could be one dead output on that relay.
Of course, verify continuity to the injectors from Pin 13 (IIRC) on the ECU. Should hit one pin on each injector.
Let us know how these tests go.
http://www.saabnet.com/tsn/bb/900/index.html?bID=150999
http://www.saabnet.com/tsn/bb/900/index.html?bID=152530
Ed S
posted by 208.148.189...
, Tue, 7 May 2002 16:49:28
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